Frequency stabilization device and atomic clock device

Abstract

To suitably stabilize the frequency of laser light.SOLUTION: A frequency stabilization device includes an electro-optical modulator 13 that modulates the phase of laser light using a modulation signal, an optical resonator 16 that resonates the laser light modulated by the electro-optical modulator 13, and a servo circuit 22 that adjusts the frequency of the laser light irradiated with by the laser device 10 on the basis of the optical resonator 16 and the modulation signal. The optical resonator 16 resonates in itself laser light having a frequency corresponding to a sideband within the frequency band of the laser light modulated by the electro-optical modulator 13.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a frequency stabilization device that stabilizes the frequency of laser light, and an atomic clock device that uses laser light irradiated from the frequency stabilization device. [Background technology]

[0002] One of the methods for stabilizing the frequency of a laser beam is the PDH (Pound-Drever-Hall) method. The PDH method uses an optical resonator to stabilize the frequency of a laser beam. In the PDH method, an electro-optic modulator (EOM) is used to stabilize the frequency f m The phase-modulated laser light enters the optical resonator. The light reflected from the optical resonator is extracted by a polarizing beam splitter (PBS) and received by a photodetector (photodiode), which gives a beat signal between the carrier and the sideband. In the PDH method, the obtained beat signal is used as an error signal for feedback control, making it possible to stabilize the frequency of the laser light at a frequency where the carrier resonates with the optical resonator. [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] RWP Drever, JL Hall, FV Kowalski, J. Hough, GM Ford, AJ Munley and H. Ward, “Laser Phase and Frequency Stabilization Using an Optical Resonator” Appl. Phys. B: Photophys. Laser Chem. 31, 97-105 (1983). Summary of the Invention [Problem to be solved by the invention]

[0004] The frequency stability using the PDH method depends on the stability of the resonator length in the optical resonator. It is desirable that the resonator length not change as much as possible. One of the factors that change the resonator length is the change in the amount of light incident on the optical resonator. The light that enters the optical resonator and travels back and forth between a pair of mirrors heats the inside of the resonator and exerts a force on the mirrors of the optical resonator due to radiation pressure. The light that enters the optical resonator generates thermal noise in the optical resonator, and this thermal noise also changes the frequency stability. Therefore, it is desirable for the signal strength of the light that enters the optical resonator to be small.

[0005] On the other hand, if the signal strength of the light incident on the optical resonator becomes smaller, when the laser light is received by the photodetector, the intensity of the interference light between the carrier and the sideband becomes smaller, and the S / N ratio of the light signal detected by the photodetector decreases. As a result, the stability of the frequency of the laser light deteriorates. In other words, there is a trade-off relationship in which the smaller the amount of light incident on the optical resonator, the more stable the resonator length in the optical resonator becomes, but the lower the S / N ratio of the light signal detected by the photodetector becomes.

[0006] The present disclosure has been made to solve such problems, and its purpose is to preferably stabilize the frequency of laser light. [Means for solving the problem]

[0007] The present disclosure relates to an atomic clock device. The atomic clock device includes a vacuum vessel, an atomic generating device that radiates an atomic beam into the vacuum vessel, a laser device that excites transitions between energy levels of atoms by irradiating a laser beam onto the vacuum vessel while the atomic beam is radiated by the atomic generating device, a detection device that detects a light intensity that occurs in proportion to the energy transition probability of the atoms generated in the vacuum vessel, a control device that specifies the frequency of the laser beam irradiated by the laser device based on the light intensity detected by the detection device, and a frequency stabilization device that stabilizes the frequency of the laser beam irradiated by the laser device. The frequency stabilization device includes a phase modulation unit that modulates the phase of the laser beam using a modulation signal, an optical resonator that resonates the laser beam modulated by the phase modulation unit, and a laser adjustment unit that adjusts the frequency of the laser beam irradiated by the laser device based on the optical resonator and the modulation signal. The optical resonator resonates the laser beam of a frequency corresponding to a sideband of the frequency band of the laser beam modulated by the phase modulation unit in the optical resonator.

[0008] The present disclosure relates to a frequency stabilizing device that stabilizes the frequency of laser light irradiated by at least one laser device. The frequency stabilizing device includes a phase modulation unit that modulates the phase of the laser light using a modulation signal, an optical resonator that resonates the laser light modulated by the phase modulation unit, and a laser adjustment unit that adjusts the frequency of the laser light irradiated by the laser device based on the optical resonator and the modulation signal. The optical resonator resonates the laser light having a frequency corresponding to a sideband in the frequency band of the laser light modulated by the phase modulation unit in the optical resonator. Effect of the Invention

[0009] According to the frequency stabilization device and atomic clock device of the present disclosure, the frequency of the laser light can be suitably stabilized by resonating the laser light having a frequency corresponding to the sideband. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a functional block diagram of an optical lattice atomic clock according to a first embodiment. [Diagram 2] FIG. 1 is a conceptual diagram of an optical lattice. [Diagram 3] 1 is a functional block diagram of a frequency stabilization device according to a first embodiment. [Figure 4] FIG. 2 is a diagram for explaining frequency components of laser light. [Diagram 5] 1 is a graph showing a simulation of an error signal; [Figure 6] 4 is a flowchart showing a frequency stabilization process of the frequency stabilization device. [Figure 7] FIG. 11 is a functional block diagram of a frequency stabilization device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present embodiment will now be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and, in principle, descriptions thereof will not be repeated.

[0012] [Embodiment 1] Fig. 1 is a functional block diagram of an atomic clock device 100 according to embodiment 1. The atomic clock device 100 in Fig. 1 is an optical lattice atomic clock (also called an optical lattice clock).

[0013] 1, the atomic clock device 100 includes an atom generating device 110, a vacuum vessel 130, a detecting device 140, a plurality of laser devices 10, a magnetic field generating device 160, a control device 170, and a frequency stabilizing device 1. The plurality of laser devices 10 include a cooling laser device 10A, an excitation laser device 10B, a detection laser device 10C, and an optical lattice laser device 10D.

[0014] The atom generator 110 includes a heating device (oven) (not shown), and heats an atomic base material such as strontium, ytterbium, or mercury in the oven. By heating, the chemical bonds between the atoms are broken, isolating the atoms and generating a group of atoms (atomic gas). Since the heated and gasified atoms have high kinetic energy, the atom generator 110 emits high-speed atomic gas as an atomic beam. The atomic beam emitted from the atom generator 110 is guided into a vacuum vessel 130.

[0015] The cooling laser device 10A is controlled by a control signal CTL1 from the control device 170. The cooling laser device 10A irradiates the atomic beam emitted from the atom generator 110 with laser light (arrows AR1 and AR2 in FIG. 1) that faces three-dimensionally in a vacuum vessel 130. By irradiating the atomic beam with this cooling laser light in a direction opposite to the direction of motion of the atomic beam, the kinetic energy of the atoms is reduced (i.e., they are cooled), and as a result, the speed of the atoms is reduced.

[0016] A pair of opposing mirrors 131, 132 are provided inside the vacuum vessel 130. When a laser beam controlled to a specific wavelength (magic wavelength) by a control signal CTL5 of the control device 170 is emitted from the laser device 10D for an optical lattice between the opposing mirrors 131, 132, a standing wave is generated between the mirrors 131 and 132 by the laser beam.

[0017] Generally, atoms are polarized in an electric field and generate induced dipoles. These dipoles interact with the electric field. As a result, in a spatially non-uniform laser electric field, the electric potential for the atoms becomes minimal at the maximum point of the electric field strength, and the atoms are captured (trapped) at that position. As described above, when a standing wave of the laser light is generated between the mirrors 131 and 132, the atoms are trapped at the antinodes of the standing wave. When these standing waves are combined three-dimensionally, an "optical lattice" in which atoms are arranged at half-wavelength intervals is realized. Figure 2 conceptually shows this optical lattice. The optical lattice 190 generated by the laser in Figure 2 is conceptually a spatial interference fringe in which concave portions of the electric potential are formed at regular intervals, and the atoms ATM are captured in the concave portions.

[0018] When atoms have momentum (velocity), the resonance frequency may shift due to the Doppler effect, which may reduce the accuracy of the measured time. By slowing down the atomic ATM in the atomic beam using the laser light of the cooling laser device 10A and capturing the atomic ATM using an optical lattice 190 as shown in Figure 2, it becomes possible to search for the resonance frequency of the atom in a stationary state.

[0019] The magnetic field generating device 160 is controlled by a control signal CTL4 from the control device 170, and applies a magnetic field to the moving atomic ATM by passing a current through electromagnetic coils (not shown) arranged around the mirrors 131 and 132 in the vacuum vessel 130. The applied magnetic field controls the energy level of the atomic ATM, contributing to cooling of various atoms.

[0020] The excitation laser device 10B is controlled by a control signal CTL2 from the control device 170. The excitation laser device 10B irradiates the trapped atomic ATM with a pulsed laser light to excite the energy transition of the atomic ATM. An atom generally has a plurality of inherent energy levels, and has a property that in the transition between two different energy levels, a photon having a frequency with an energy corresponding to the energy level difference is selectively absorbed.

[0021] The detection laser device 10C is controlled by a control signal CTL3 from the control device 170. The detection laser device 10C irradiates the atomic ATM with a detection laser beam after the energy level of the atomic ATM is excited by the excitation laser device 10B. The laser irradiated from the detection laser device 10C generates fluorescence having an intensity proportional to the energy transition probability of the atom.

[0022] The detection device 140 receives the fluorescence generated by the detection laser device 10C and detects the intensity of the received fluorescence. The detection device 140 outputs to the control device 170 a transition probability spectrum that depends on the excitation laser frequency and is represented by the detected fluorescence intensity.

[0023] The control device 170 is configured to include, for example, a CPU (Central Processing Unit), a memory, and an input / output interface (none of which are shown), and performs overall control of each device of the atomic clock device 100. The control device 170 identifies the resonance frequency of the atomic ATM from the transition probability spectrum received from the detection device 140. The control device 170 also stabilizes the frequency of the laser light irradiated from the excitation laser device 10B based on the resonance frequency found by calculation.

[0024] The frequency stabilizing device 1 is a device for stabilizing the frequency of laser light irradiated from the laser device 10. In the first embodiment, a case will be described in which the frequency of laser light irradiated from the excitation laser device 10B among the multiple laser devices 10 is stabilized. The frequency stabilizing device 1 may stabilize the frequency of laser light irradiated from the laser devices 10 other than the excitation laser device 10B, such as the cooling laser device 10A, the excitation laser device 10B, the detection laser device 10C, and the optical lattice laser device 10D, or may stabilize frequencies corresponding to multiple types of laser devices.

[0025] In an atomic clock device 100 including such an optical lattice atomic clock, highly accurate frequency stabilization of laser light is required. The frequency stabilization device 1 can suitably stabilize the laser light irradiated from, for example, the excitation laser device 10B among the multiple laser devices 10. Figure 3 is a functional block diagram of the frequency stabilization device 1 according to the first embodiment.

[0026] Referring to FIG. 3, the frequency stabilization device 1 includes an isolator 12, an electro-optical modulator (EOM) 13, a polarizing beam splitter (PBS) 14, a quarter-wave plate 15, an optical resonator 16, a photodiode (PD) 17, an RF oscillator 18, a phase shifter 19, a phase comparator 20, a low-pass filter (LPF) 21, and a servo circuit 22.

[0027] The isolator 12 is provided in the optical path between the laser device 10 and the optical resonator 16. The isolator 12 is a device that transmits laser light only in a fixed direction. By arranging the isolator 12 near the laser device 10, it is possible to prevent instability of the frequency of the laser light caused by return light. The electro-optical modulator 13 functions as a phase modulation section that modulates the phase of the laser light. The electro-optical modulator 13 is capable of electrically changing the refractive index of light. The electro-optical modulator 13 modulates the frequency and phase of the laser light based on a modulation signal input from the RF oscillator 18.

[0028] The polarizing beam splitter 14 transmits a portion of the incident laser light, and reflects the laser light returning via the quarter-wave plate 15 in a direction approximately perpendicular to the incident laser light. The quarter-wave plate 15 changes the polarization state of the laser light incident from the polarizing beam splitter 14 and causes it to enter the optical resonator 16, and also changes the polarization state of the laser light returning from the optical resonator 16 and returns it to the polarizing beam splitter 14.

[0029] The photodiode 17 functions as a light detection unit that detects a part of the laser light reflected by the polarizing beam splitter 14 as a detection signal. The photodiode 17 outputs an electric signal according to the intensity of the laser light. The RF oscillator 18 functions as an oscillation unit that outputs a modulation signal. The RF oscillator 18 outputs the modulation signal to the electro-optic modulator 13 and the phase shifter 19.

[0030] The phase shifter 19 shifts the phase of the modulated signal transmitted from the RF oscillator 18 by 180 degrees. The phase comparator 20 functions as a phase comparator that calculates a comparison value between the detection signal detected by the photodiode 17 and the modulated signal from the RF oscillator 18. The phase comparator 20 calculates an error from the detection signal and the modulated signal using information on the difference between the frequency of the optical resonator 16 and the frequency of the laser light as a comparison value. The comparison value is passed through a low-pass filter 21, whereby an error signal based on the error is generated.

[0031] The servo circuit 22 functions as a laser adjustment unit that uses the error signal to adjust the frequency of the laser light irradiated by the laser device 10. For example, the servo circuit 22 performs feedback control to reduce the error by adjusting the frequency of the laser light to the resonator length of the optical resonator 16 in the laser device 10.

[0032] The optical resonator 16 resonates the laser light modulated by the electro-optical modulator 13. The optical resonator 16 has a pair of mirrors therein to resonate the laser light modulated by the electro-optical modulator 13. The pair of mirrors has a high reflectance (for example, about 99.9%) so that the light leaking out of the optical resonator 16 is extremely weak. The number of mirrors arranged inside the optical resonator 16 is not limited to two, and may be three or more. In other words, the resonator may be one in which the mirrors are arranged so that the light is reflected between each other, or one in which the mirrors are arranged in a ring shape so that the light is reflected in one direction.

[0033] A piezoelectric element (piezoelectric element) is disposed on the mirror. The piezoelectric element drives the mirror constituting the optical resonator 16 in accordance with a command from the control device 170, thereby displacing the mirror in the optical axis direction. This makes it possible to change the resonator length of the optical resonator 16. Therefore, it is possible to vary the resonator length so as to match the laser wave number, and also to sweep the laser wave number so as to match the resonator length.

[0034] Here, a half mirror 11 is disposed between the laser device 10 and the isolator 12 of the frequency stabilization device 1. The half mirror 11 passes a portion of the incident laser light and reflects the remaining laser light in a direction substantially perpendicular to the laser light. The half mirror 11 functions as a guide portion that guides a portion of the stabilized laser light toward the inside of the vacuum vessel 130 of the atomic clock device 100.

[0035] In this way, the frequency stabilization device 1 is configured to input the phase-modulated laser light to the optical resonator 16, detect the laser light output from the optical resonator 16 with the photodiode 17, and apply feedback based on the detected laser light, thereby stabilizing the frequency of the laser light. Since the stability of the frequency by such a PDH method depends on the stability of the resonator length in the optical resonator, it is desirable that the resonator length not change as much as possible.

[0036] For example, light entering an optical resonator generates thermal noise in the optical resonator, and this thermal noise also changes the frequency stability, so it is desirable for the signal strength of the light entering the optical resonator to be small. On the other hand, if the signal strength of the light entering the optical resonator is small, when the laser light is received by the photodetector, the intensity of the interference light between the carrier and the sideband becomes small, and the S / N ratio of the signal decreases. As a result, the stability of the frequency of the laser light deteriorates. In other words, there is a trade-off relationship in which the smaller the amount of light entering the optical resonator, the more stable the resonator length in the optical resonator becomes, but the lower the S / N ratio of the light signal detected by the photodetector becomes.

[0037] Therefore, as described below, the frequency stabilization device 1 according to the embodiment is configured to use light corresponding to the sideband, not light corresponding to the carrier, as the laser light incident on the optical resonator 16. The optical resonator is configured to resonate laser light of a frequency corresponding to the sideband, among the frequency band of the laser light modulated by the phase modulation unit.

[0038] The frequency components of the laser light will be specifically described. FIG. 4 is a diagram for explaining the frequency components of the laser light. The laser light before entering the electro-optical modulator 13 is represented as a spectrum in which the carrier has a single peak, as shown in FIG. 4(A). After that, the RF oscillator 18 outputs a modulation signal to the electro-optical modulator 13, which allows the laser light of a frequency corresponding to the sideband to resonate in the optical resonator 16. As a result, the laser light after being phase-modulated in the electro-optical modulator 13 is represented as a spectrum with three peaks, as shown in FIG. 4(B). The peaks located on both sides of the central carrier are the sidebands.

[0039] In the optical resonator 16 shown in Fig. 4(C), a laser beam having a frequency corresponding to a sideband among the frequency band of the laser beam modulated by the electro-optic modulator 13 is resonated. In the present disclosure, a sideband is used instead of a carrier as the laser beam to be resonated in the optical resonator 16. For example, the sideband is resonated in the optical resonator 16 by adjusting the oscillation frequency of the laser device 10. By making the light incident on the optical resonator 16 a sideband having a signal intensity lower than that of the carrier, the resonator length in the optical resonator 16 can be stabilized.

[0040] In the photodiode 17, a beat signal between the carrier and the sideband is obtained in the same way as when the carrier is resonated in the optical resonator 16. This is because the signal strength of the carrier is large, so the intensity of the interference light can be secured. This makes it possible to prevent the S / N ratio of the signal obtained by the photodiode 17 from decreasing.

[0041] Here, the problem of resonating the sideband will be described. FIG. 5 is a graph showing a simulation of an error signal. In FIG. 5, a simulation is performed so that the carrier coincides with the resonant frequency of the optical resonator 16. In the frequency stabilization process, the zero crossing point (the point where the error signal becomes zero) with the waveform of the error signal becomes the lock point of the frequency used in the optical resonator 16. As shown in FIG. 5, the zero crossing point corresponding to the central carrier has a negative slope. As shown in FIG. 5, the zero crossing points corresponding to the sidebands on both ends of the central point have a positive slope.

[0042] That is, the slope of the error signal is inverted between the carrier and the sideband. For this reason, when using the sideband, the phase must be inverted by 180 degrees in the phase shifter 19. The phase comparator 20 calculates a comparison value by comparing the detection signal detected by the photodiode 17 with the modulated signal from the RF oscillator 18, the phase of which is inverted by 180 degrees. This makes it possible to generate an appropriate error signal.

[0043] Next, the flow of the frequency stabilization process executed in the frequency stabilization device 1 will be described. FIG. 6 is a flowchart showing the frequency stabilization process of the frequency stabilization device 1. In the following, each step in the flowchart will be simply denoted as "S". The frequency stabilization device 1 modulates the phase of the laser light in the electro-optic modulator 13, which is a phase modulation section (S1). Next, the frequency stabilization device 1 resonates the laser light of a frequency corresponding to a sideband in the frequency band of the laser light in the optical resonator 16 (S2). Next, the frequency stabilization device 1 outputs a detection signal corresponding to the sideband in the photodiode 17, which is a light detection section (S3).

[0044] Next, the frequency stabilizing device 1 calculates an error using information on the difference between the frequency of the optical resonator 16 and the frequency of the laser light as a comparison value in the phase comparator 20, which is a phase comparison unit (S4). Next, the frequency stabilizing device 1 stabilizes the laser light in the servo circuit 22, which is a laser adjustment unit (S5).

[0045] By operating the frequency stabilization device 1 according to the above flow, it is possible to resonate the laser light having a frequency corresponding to the sideband in the frequency band of the laser light modulated by the electro-optic modulator 13 in the optical resonator 16. By making the light incident on the optical resonator 16 a sideband having a smaller signal intensity than the carrier, it is possible to stabilize the resonator length in the optical resonator 16. In addition, by detecting a beat signal between the carrier and the sideband in the photodiode 17, it is possible to prevent the S / N ratio of the signal obtained by the photodiode 17 from decreasing.

[0046] [Embodiment 2] A frequency stabilizing device 1A according to the second embodiment will be described. Fig. 7 is a functional block diagram of the frequency stabilizing device 1A according to the second embodiment. The configuration of the frequency stabilizing device 1A according to the second embodiment is the same as that of the frequency stabilizing device 1 according to the first embodiment. The second embodiment is different from the first embodiment in that two laser devices 10 are provided.

[0047] The frequency stabilizing device 1A stabilizes the frequencies of laser light emitted from two of the multiple laser devices 10. The frequency stabilizing device 1A may stabilize the frequencies of laser light emitted from three or more laser devices.

[0048] The electro-optical modulator 13 of the frequency stabilization device 1A can modulate the frequency and phase of multiple laser beams. The optical resonator 16 resonates the laser beam of a frequency corresponding to the sideband in the frequency band of the laser beam modulated by the electro-optical modulator 13 for each laser beam. Then, the photodiode 17 detects the beat signal between the carrier and the sideband for each laser beam. Note that multiple laser beams are simultaneously incident on the optical resonator 16, but the resonator length is fixed at a constant value. This is because the oscillation frequency of the laser beam irradiated from each laser device 10 is adjusted to the resonant frequency of the optical resonator 16 so as to resonate in the sideband.

[0049] The frequency stabilization device 1A resonates laser light having a frequency corresponding to a sideband in a plurality of laser lights. As a result, even when a plurality of laser lights are used, the resonator length in the optical resonator 16 can be stabilized by making the light incident on the optical resonator 16 a sideband having a smaller signal intensity than the carrier. In addition, by detecting a beat signal between the carrier and the sideband for each laser light in the photodiode 17, it is possible to prevent the S / N ratio of the signal obtained by the photodiode 17 from decreasing.

[0050] (Modification) In the above embodiment, the case has been described where the oscillation frequency of the laser device 10 is changed and the cavity length of the optical resonator 16 is kept constant. However, the oscillation frequency of the laser device 10 may be fixed and the cavity length of the optical resonator 16 may be changed to a length corresponding to the frequency corresponding to the sideband.

[0051] <Application to other atomic clocks> In the above embodiment, an example has been described in which a method for stabilizing the frequency of a laser beam is applied to an optical lattice atomic clock. However, the concept of the features of the present disclosure can also be applied to other types of atomic clocks other than optical lattice atomic clocks. For example, a method for stabilizing the frequency of a laser beam may be applied to a laser beam used in an atomic fountain microwave atomic clock, an atomic beam microwave atomic clock, a photoion clock, etc.

[0052] [Aspects] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0053] (Item 1) An atomic clock device according to one embodiment includes a vacuum vessel, an atom generating device that radiates an atomic beam into the vacuum vessel, a laser device that excites transitions between energy levels of atoms by irradiating the vacuum vessel with laser light while the atomic beam is radiated by the atom generating device, a detection device that detects light intensity that occurs in proportion to the probability of energy transition of the atoms generated in the vacuum vessel, a control device that specifies the frequency of the laser light irradiated by the laser device based on the light intensity detected by the detection device, and a frequency stabilization device that stabilizes the frequency of the laser light irradiated by the laser device. The frequency stabilization device includes a phase modulation unit that modulates the phase of the laser light using a modulation signal, an optical resonator that resonates the laser light modulated by the phase modulation unit, and a laser adjustment unit that adjusts the frequency of the laser light irradiated by the laser device based on the optical resonator and the modulation signal. The optical resonator resonates in the optical resonator a laser light of a frequency corresponding to a sideband in the frequency band of the laser light modulated by the phase modulation unit.

[0054] According to the atomic clock device described in paragraph 1, when the frequency stabilizing device stabilizes the frequency of the laser light irradiated from the laser device, the light corresponding to the sideband among the frequency band of the laser light modulated by the phase modulation unit can be resonated in the optical resonator. By using the light corresponding to the sideband, which has a smaller signal intensity than the light corresponding to the carrier, as the light incident on the optical resonator, the resonator length in the optical resonator can be stabilized. On the other hand, even if the light incident on the resonator is changed from the light corresponding to the carrier to the light corresponding to the sideband, the intensity of the interference light can be secured to a certain degree as long as the signal intensity of either the carrier or the sideband is large, so that the S / N ratio of the signal can be prevented from decreasing. This enables accurate timekeeping using laser light with a stable frequency.

[0055] (Item 2) According to the atomic clock device described in item 1, the frequency stabilization device further includes an oscillator that outputs a modulation signal, an optical detector that detects a part of the laser light output from the optical resonator as a detection signal, and a phase comparator that calculates a comparison value between the detection signal and the modulation signal. The laser adjustment unit adjusts the frequency of the laser light irradiated by the laser device based on the comparison value.

[0056] According to the atomic clock device described in paragraph 2, the frequency of the laser light irradiated by the laser device can be adjusted based on the comparison value between the detection signal and the modulation signal. This makes it possible to suitably stabilize the frequency of the laser light.

[0057] (Item 3) According to the atomic clock device described in item 1 or 2, the optical resonator section can change the resonator length to a length corresponding to the frequency corresponding to the sideband.

[0058] According to the atomic clock device described in the third aspect, the resonator length of the optical resonator can be changed to a length corresponding to the frequency corresponding to the sideband, thereby making it possible to suitably stabilize the frequency of the laser light.

[0059] (Item 4) According to the atomic clock device described in any one of items 1 to 3, the frequency stabilization device further includes a guidance section that is disposed between the laser device and the phase modulation section and that guides a portion of the laser light irradiated by the laser device to the atomic clock device.

[0060] According to the atomic clock device described in paragraph 4, a part of the laser light with a stabilized frequency can be sent to the atomic clock device by the induction unit. This enables accurate timekeeping using the laser light with a stable frequency.

[0061] (Item 5) According to the atomic clock device described in any one of Items 1 to 4, the laser device includes a first laser device that irradiates a first laser light having a first wavelength, and a second laser device that irradiates a second laser light having a second wavelength. The frequency stabilization device stabilizes the frequency of each of the first laser light and the second laser light.

[0062] According to the atomic clock device described in item 5, it is possible to stabilize the frequency of each of the first laser light and the second laser light.

[0063] (Item 6) According to the atomic clock device described in any one of items 2 to 5, the oscillator outputs to the phase modulator a modulation signal that enables laser light having a frequency corresponding to a sideband to resonate in the optical resonator.

[0064] According to the atomic clock device described in paragraph 6, an appropriate modulation signal that enables the laser light of a frequency corresponding to the sideband to resonate in the optical resonator can be transmitted from the oscillator to the phase modulator, thereby making it possible to suitably stabilize the frequency of the laser light.

[0065] (Item 7) According to the atomic clock device described in any one of items 2 to 6, the phase comparison unit calculates a comparison value by comparing the detection signal with a modulated signal whose phase is inverted by 180 degrees.

[0066] According to the atomic clock device described in item 7, it is possible to calculate a comparison value corresponding to a sideband, thereby making it possible to suitably stabilize the frequency of the laser light.

[0067] (Item 8) A frequency stabilization device for stabilizing the frequency of laser light irradiated by at least one laser device according to one embodiment includes a phase modulation unit for modulating the phase of the laser light using a modulation signal, an optical resonator for resonating the laser light modulated by the phase modulation unit, and a laser adjustment unit for adjusting the frequency of the laser light irradiated by the laser device based on the optical resonator and the modulation signal. The optical resonator resonates in the optical resonator a laser light having a frequency corresponding to a sideband within the frequency band of the laser light modulated by the phase modulation unit.

[0068] According to the frequency stabilization device described in paragraph 8, when the frequency stabilization device stabilizes the frequency of the laser light irradiated from the laser device, the light corresponding to the sideband among the frequency band of the laser light modulated by the phase modulation unit can be resonated in the optical resonator. By using the light corresponding to the sideband, which has a smaller signal intensity than the light corresponding to the carrier, as the light incident on the optical resonator, the resonator length in the optical resonator can be stabilized. On the other hand, even if the light incident on the resonator is changed from the light corresponding to the carrier to the light corresponding to the sideband, the intensity of the interference light can be secured to a certain degree as long as the signal intensity of either the carrier or the sideband is large, so that the S / N ratio of the signal can be prevented from decreasing.

[0069] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0070] 1,1A frequency stabilization device, 10 laser device, 10A cooling laser device, 10B excitation laser device, 10C detection laser device, 10D laser device for optical lattice, 11 half mirror, 12 isolator, 13 electro-optic modulator, 14 polarizing beam splitter, 15 1 / 4 wave plate, 16 optical resonator, 17 photodiode, 18 RF oscillator, 19 phase shifter, 20 phase comparator, 21 low-pass filter, 22 servo circuit, 100 atomic clock device, 110 atomic generator, 130 vacuum vessel, 131,132 mirror, 140 detection device, 160 magnetic field generator, 170 control device, 190 optical lattice.

Claims

1. 1. An atomic clock apparatus, comprising: A vacuum vessel; an atom generator for emitting an atomic beam into the vacuum vessel; a laser device that excites transitions between energy levels of atoms by irradiating the vacuum vessel with laser light while the atomic beam is being emitted by the atom generating device; a detection device for detecting a light intensity generated in proportion to an energy transition probability of the atoms generated in the vacuum vessel; a control device that specifies a frequency of the laser light irradiated by the laser device based on the light intensity detected by the detection device; a frequency stabilization device that stabilizes the frequency of the laser light irradiated by the laser device, The frequency stabilization device includes: a phase modulation unit that modulates the phase of the laser light using a modulation signal; an optical resonator that resonates the laser light modulated by the phase modulation unit; a laser adjustment unit that adjusts a frequency of the laser light irradiated by the laser device based on the optical resonator and the modulation signal, The optical resonator resonates the laser light having a frequency corresponding to a sideband of the frequency band of the laser light modulated by the phase modulator in the optical resonator.

2. The frequency stabilization device includes: an oscillator for outputting the modulated signal; a light detection unit that detects a part of the laser light output from the optical resonator as a detection signal; a phase comparator that calculates a comparison value between the detection signal and the modulation signal, 2. The atomic clock device according to claim 1, wherein the laser adjustment section adjusts a frequency of the laser light emitted by the laser device based on the comparison value.

3. 3. The atomic clock device according to claim 1, wherein the optical resonator portion is capable of changing a resonator length to a length corresponding to a frequency corresponding to the sideband.

4. 3. The atomic clock device according to claim 1, wherein the frequency stabilization device further comprises a guidance section disposed between the laser device and the phase modulation section and configured to guide a portion of the laser light irradiated by the laser device to the atomic clock device.

5. the laser device includes a first laser device that irradiates a first laser beam having a first wavelength and a second laser device that irradiates a second laser beam having a second wavelength; 3. The atomic clock device according to claim 1, wherein the frequency stabilization device stabilizes the frequency of each of the first laser light and the second laser light.

6. 3. The atomic clock device according to claim 2, wherein the oscillation section outputs to the phase modulation section the modulation signal that allows the laser light having a frequency corresponding to the sideband to resonate in the optical resonator.

7. 3. The atomic clock device according to claim 2, wherein the phase comparator calculates the comparison value by comparing the detection signal with the modulation signal whose phase is inverted by 180 degrees.

8. A frequency stabilization device for stabilizing a frequency of laser light irradiated by at least one laser device, comprising: a phase modulation unit that modulates the phase of the laser light using a modulation signal; an optical resonator that resonates the laser light modulated by the phase modulation unit; a laser adjustment unit that adjusts a frequency of the laser light irradiated by the laser device based on the optical resonator and the modulation signal, The optical resonator resonates the laser light having a frequency corresponding to a sideband of the frequency band of the laser light modulated by the phase modulator in the optical resonator.

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